1. Field of the Invention
The present invention relates to a filter circuit having a biquadratic transfer function which comprises resistors, capacitors and an operational amplifier and which exhibits a through-line lying at a reference potential.
2. Description of the Prior Art
A series of basic circuits for the construction of active filter circuits have already become known in the art. Among other things, it is known to realize active filter circuits, without coils, with the assistance of operational amplifiers. In this connection, a circuit of this type is disclosed in the essay "Single Amplifier Functionally Tunable Low-Pass-Notch Filter" by Stalin A. Boctor (IEEE Transactions of Circuits and Systems, Vol. CAS-22, No. 11, Nov. 1975, pp. 875-881, particularly Page 887 and FIG. 3) which allows a low-pass transfer function of the second degree to be realized with only one operational amplifier. However, it is evident that this known circuit is only suitable for the representation of low-pass transfer functions. Further, in order to attain a sufficient quality, a capacitance relationship of the two capacitors is required in this circuit, which deviates very strongly from the value one and can only be realized with great difficulty, particularly upon construction in layer technology.